Thayer Watkins
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Global Warming and the Thermohaline Circulation:
A negative feedback mechanism

The thermohaline circulation takes place when saltier, denser water in the North Atlantic sinks thus drawing in water from the Gulf Stream. It is part of the very complex climate system of the Earth in general and the Arctic in particular.

The Arctic is a region with a radiation deficit. It radiates more energy into space than it receives from the Sun. This deficit is covered by the convection of heat energy from warmer regions. If that convection of heat into the Arctic were reduced then the Arctic temperature would decline and thus its radiation of energy into space would decrease until a balance is reached. On the other hand if the net inflow of energy into the Arctic is increased then the temperatures would rise, again until a new balance is reached.

If the effects of an increase in Arctic temperatures results in a reduction of the convection of heat into the Arctic then the new balance reached for a net increase in radiation energy would involve less of a change in temperature than would occur without that reduction in convection. It is a simple case of negative feedback. This process is depicted in the following diagrams. First consider the case of no feedback.

The red line represents the amount of energy in the form of heat being brought into the Arctic. For this first case this is presumed to be constant over time. In the diagram it is supposed that the net radiation energy flow has increased at time zero such that the combined radiation and convection inflows (the yellow line) are greater than the radiation outflow which is shown as a light blue line. The net heat inflow causes the temperature to rise and thus also the radiation outflow. The radiation outflow rises until it reaches the level of the energy inflow. In reality the radiation outflow would rise and approach a balance with the energy inflow asymptotically. For purposes of illustration the radiation outflow is shown increasing linearly and achieving equality with the energy inflow in some finite time.

If the rising temperature is producting meltwater that interferes with the convection inflow of heat then part of the increased net radiation inflow is offset by a decline in the convection inflow as shown in the following diagram.

As the radiation outflow rises the inflow is declining so the balance between energy outflow and energy inflow is reached sooner than in the first case. Thereafter the decline in convection inflow is halted and an equilibrium is maintained. This is the normal case with negative feedback process.

Instead of this normal negative feedback mechanism the global warming alarmists are trying to put over the process depicted in the following diagram.

Here the rising temperature produces no feedback until the Arctic ice is melted then suddenly the the thermohaline circulation is shut down including the Gulf Stream. The convection heat inflow suddenly drops and with it the net energy inflow. The radiation outflow then has to drop to match the decreased energy inflow. Thus this scenario has the end result of a lower temperature and energy outflow than was the initial state. This is a ridiculous scenario that only true believers of a quasi-religious dogma could accept and only charlatans could promote.

Climatological questions should be dealt with on an empirical level because the climate system is so complex that perfectly plausible theoretical arguments are often incorrect. What is the empirical evidence? First consider the matter of the extent of seaice in the Arctic.

Although the general trend is downward over the period shown the levels were lower in the 1930's yet recovered. It is also notable that from 1994 to 1995 the area decreased by about seven hundred thousand square kilometers yet it increased the next year by about five hundred thosand square kilometers and by 2001 was back up to normal. The melting of seven hundred thousand square kilometers of sea ice from 1994 to 1995 apparently had no effect on the Gulf Stream and the thermohaline circulation it represents.

It is notable that if the fluctuations in Arctic ice are due to global warming then there should be a similiar decline in seaice in the Antarctic but instead in the Antarctic there has been an increase in sea ice such that there has been essentially no change in sea ice in the polar regions of the Earth. For more on this see Polar Ice.

Although there has been warming in the Arctic region the amount is far less than what is predicted by the global climate models. Those models project temperature increases in the polar regions of three to four times the global average. The temperature increase in the Arctic has been about 80 percent larger than the global average but temperature have been declining in the Antarctic rather that increase three to four times the global average. For more on this matter see Polar Warming.

Even within the Arctic region there are subregions experiencing downward trending temperatures including the area of Greenland which is the most relevant region concerning effects on the thermohaline circulation.

Deviation of Temperatures from Average
in the Greenland Region

The general trend has been downward. One can of course find intervals over which that trend seems to be upward but selectivity is possible with even random numbers and represents a creation of a trend by the observer rather than something that is in the data.

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